2.4 Exposure
The primary exposure of interest was baloxavir prescription. We selected
oral and inhaled neuraminidase inhibitors (NAIs) as the active
comparator, namely oseltamivir, zanamivir and laninamivir. Intravenous
NAI treatment was not considered as a comparator because recipient for
this form might have the different characteristic (eg, severity) from
those receiving baloxavir and other forms of NAIs. Within the same
disease course, a few patients (<0.1%) received a different
type of antiviral drug or more than one type. We assigned these patients
to the antiviral group according to the first prescribed class (since
the second drug was unlikely to be prescribed within 48 hours of symptom
onset). All prescribed drugs, including antivirals, were identified by
drug code and brand name (when necessary) from the database. All
anti-influenza drugs investigated are covered by insurance for the
treatment of influenza, but not covered for prevention.